This invention relates to concept of transferring information in a computer program product for use with a computer system having a main storage device in processing communication with a plurality of input/output devices.
In a network computing environment, multitudes of commands and requests for retrieval and storage of data are processed every second. To properly address the complexity of routing these commands and requests, a number of different resolutions have been implemented. In some data processing architectures, such as International Business Machines Enterprise System Architecture/390 (Enterprise System Architecture/390 is a registered trademark of International Business Machines Corporation), a channel subsystem is utilized to pass information between the main storage and input/output (I/O) devices. The channel subsystem includes one or more channel paths, each including one or more channels and one or more control units. Recently developed technologies such as the International Business Machines ESCON switch (ESCON is a registered trademark of International Business Machines Corporation), connect the I/O devices to the main memory through the control units using legacy channels to support the data transfer there between.
But as the technology improves, the performance of new system processors will require many more legacy channels than are presently in use to support the resulting increase of information transfer in the data processing systems. Current architectural constraints make the addition of such legacy channels an expensive proposition. A further challenge is to provide the link data rate required to support the data rates of new I/O devices such as DASDs and Tapes. In this case, simply adding more legacy channels does not adequately address the problem. A new architecture is needed that can scale up to the higher link speeds needed for normal transaction processing. Therefore, any new proposed architecture, must include a capacity to accommodate higher bandwidth channel links such as Fiber Channel links while providing better data rates and higher link speeds.
This application incorporates by reference U.S. Pat. No. 5,526,484 to Casper et. al.
In Fiber Channel computer systems comprising a Host Channel, a Fiber Fabric (including Fiber Links), and a control unit, a channel can share fabric resources. When a channel is in communication with a control unit device, a logical entity provides the pathway, the entity is called an exchange. There is overhead in creating an exchange and also in closing an exchange. The present invention provides a method to allow exchanges to remain open (if the channel determines there is no need to close it) while a channel is disconnecting from the device. Thus, in a significant number of instances, the overhead in managing the exchange pair is avoided.
It is therefore an object of the present invention to provide a method to logically disconnect without closing an exchange pair in a fiber channel connection. The method comprises transmitting a status information unit from a control unit to a channel indicating the control unit is logically disconnecting from the channel and the channel can elect to close the exchange; transmitting a status accepted information unit from the channel to the control unit indicating the outbound exchange status; and transmitting a device acknowledgement information unit from the control unit to the channel.
It is yet another object of the present invention to provide a method to logically disconnect without closing an exchange pair in a fiber channel connection comprising. The method comprising: receiving a status information unit from a control unit to a channel indicating the control unit is logically disconnecting from the channel and the channel can elect to close the exchange; receiving a status accepted information unit from the channel to the control unit indicating the outbound exchange status; and receiving a device acknowledgement information unit from the control unit to the channel.